@article{JRAM_1991__418_153333,
     author = {G.J. Martin and F.W. Gehring},
     title = {Inequalities for {M\"obius} transformations and discrete groups.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {31--76},
     publisher = {mathdoc},
     volume = {418},
     year = {1991},
     zbl = {0722.30034},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1991__418_153333/}
}